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Part 2

Part 2. -Converters by : Hamid Mala. content. Delta modulation Noise shaping Delta-sigma modulators continous-time & discrete-time passband delta-sigma modulators. Delta modulation. Delta modulation is based on quantizing the change in the signal from sample to sample.

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Part 2

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  1. Part 2 -Convertersby : Hamid Mala

  2. content • Delta modulation • Noise shaping • Delta-sigma modulators • continous-time & discrete-time • passband delta-sigma modulators

  3. Delta modulation • Delta modulation is based on quantizing the change in the signal from sample to sample

  4. Delta modulation/demodulation

  5. Delta modulation • Delta modulators, furthermore, exhibit slope overload for rapidly rising input signals, and their performance is thus dependent on the frequency of the input signal.

  6. Sigma-delta modulation and noise shaping

  7. ΔΣ modulation Only one integrator • Block diagram of ΔΣ modulator

  8. ΔΣ modulation • advantages: • unlike delta modulators, these systems encode the integral of the signal itself and thus their performance is insensitive to the rate of change of the signal. • noise shaping

  9. Continuos time ΔΣ modulation

  10. ΔΣ modulation : noise shaping • The modulator’s main action: • it lowpass-filters the signal and highpass filters the noise. • In other words the S-D loop pushes the noise into a higher frequency band.

  11. ΔΣ A/D converter • block diagram of first-order Sigma-Delta A/D converter

  12. ΔΣ A/D converter • Analysis of ΣΔ modulation in the Z-transform domain Quantization noise is modeled as additive noise sourse

  13. Continuos & discrete-time ΔΣ mod.

  14. ΔΣ A/D converter • the differentiator (1-z-1) doubles the power of quantized noise • in-band quantization noise is removed out of band

  15. ΔΣ A/D converter

  16. ΣΔ modulation • Higher oreder noise shaper has less baseband noise Rest of frequency band will be removed by digital decimation filters

  17. ΔΣ A/D converter • The output of the modulator is a coarse quantization of the analog input. • the modulator is oversampled at a rate that is as much as 64 times higher than the Nyquist rate for the DSP56ADC16 • High resolution is achieved by averaging over 64 data points to interpolate between the coarse quantization levels

  18. ΔΣ A/D converter • Digital decimation filtering • Remove shaped quantization noise • Decimation • Anti-aliasing • The simplest and most economical filter to reduce the input sampling rate is a “Comb Filter”. • the filter coefficients are all unity so does not require a multiplier • is not very effective at removing the large volume of out-of-band quantization noise generated by the S-D modulators and is seldom used in practice without additional digital filters.

  19. ΔΣ A/D converter • Comb filter design as a decimator

  20. ΔΣ A/D converter • One stage comb filtering process • no multiplier • no storage for filter coefficient • regular

  21. ΔΣ A/D converter Transfer function of a comb filter

  22. ΔΣ A/D converter

  23. Toward bandpass ΔΣ ADC

  24. bandpass ΔΣ ADC • Digitation of IF signals can be accomplished with: • Nyquist-Rate A/D Converters (Reduce the quantization noise in the whole Nyquist Band) • Bandpass SD A/D Converters (Reduce the noise only in the band of interest)

  25. Sampling of bandpass signals

  26. bandpass ΔΣ ADC • Bandpass ΔΣModulator combine: • Oversampling,M , to decrease the quantization noise in the signal band,BW • Filtering, NTF (z ), for shaping the quantization noise.

  27. bandpass ΔΣ ADC

  28. bandpass ΔΣ ADC

  29. bandpass ΔΣ ADC • Dynamic range

  30. LP ΔΣ to BP ΔΣ transformation

  31. LP to BP transformation method I • Example: applying the transformation to a 4th-order (2-2) cascade architecture

  32. LP to BP transformation method I • Example: applying the transformation to a 4th-order (2-2) cascade architecture

  33. LP and BP • for comparable performance the bandpass modulator would be required to have twice the order,and, thus, twice the complexity, of each lowpass modulator • the bandwidth of the sample-and-hold circuitry must be high enough to handle the increased center frequency.

  34. Refrences 1) Delta–Sigma Data Conversion in WirelessTransceivers Ian Galton, Member, IEEE 2)Principles of Sigma-Delta Modulation for Analog-to-Digital Converters Applications Digital Signal Processor Operation Motorola Digital SignalProcessors By Sangil Park, Ph. D.Strategic

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